The invention relates to a process for preparing optically active 1-(4-methoxybenzyl)-1,2,3,4,5,6,7,8-octahydroisoquinoline.
Optically active enantiomers of methoxybenzyloctahydroisoquinoline are useful intermediates for preparing pharmacologically active compounds such as optically active 3-methoxy-17-methylmorphinans which find utility as antitussives and analgesics.
Separation of enantiomers at an early stage of morphinan synthesis and if desired the return of the undesired isomer is of great importance to the economics of the process of preparation.
There are already various known processes for the optical resolution of (R,S)-1-(4-methoxybenzyl)-octahydroisoquinoline. Brossi and Schnider, Helv. Chim. Acta 39 (1965) 1376-86, described the separation by means of fractional crystallisation of the diastereoisomeric D-(-)-mandelic acid salts. German Pat. No. 2,003,486 discloses the separation into the antipodes by means of optically active (-)-di-O-isopropylidine-2-keto-L-gulonic acid.
These processes have the disadvantage that their implementation requires a costly optically active resolution reagent which is only available in one enantiomeric form and, after the optical resolution has been effected, is only incompletely regenerable again.